Nucleating agents for photographic reversal processes

ABSTRACT

Chelated stannous ion silver halide nucleating agents are used in photographic reversal processes. The nucleating agents are useful in reversal developer solutions or in prebaths employed prior to reversal development. The nucleating agents are especially useful for processing multilayer color products where the emulsion layers contain color couplers or for selective reversal processing of multilayer color products where the couplers are present in the color developing solutions.

United States Patent [72] Inventors Charleton C. Bard;

Arthur D. Kuh; Richard J. Malloy, all of Rochester, N.Y.

[21] Appl. No. 38,492 A [22] Filed May 18, 1970 [45] Patented Nov. 2,197 1 [73] Assignee Eastman Kodak Company Rochester, N.Y.

Continuation-impart of application SertNo. 803,941, Mar. 3, 1969, nowabandoned.

[54] NUCLEATING AGENTS FOR PHOTOGRAPHIC '51 int. ci eases/5r; [50] Fieldof Search 96/22, 59

[56] References Cited UNITED STATES PATENTS 1,552,791 9/1935 Capstaff96/59 Primary Examiner-Norman G. Torchin Assistant Examiner-Alfonso T.SuroPico Attorneys-Walter O. Hodsdon and Wendell l-l. McDowell ABSTRACT:Chelated stannous ion silver halide nucleating agents are used inphotographic reversal processes. The nucleating agents are useful inreversal developer solutions or in prebaths employed prior to reversaldevelopment. The nucleating agents are especially useful for processingmultilayer color products where the emulsion layers contain colorcouplers or for selective reversal processing of multilayer colorproducts where the couplers are present in the color developingsolutions.

NUCLEATING AGENTS FOR PHOTOGRAPHIC REVERSAL PROCESSES This applicationis a continuation-in-part of U.S. Pat. application Ser. No. 803,941filed Mar. 3, 1969, and now abandoned. This invention relates to animproved method of photographic processing, and more particularly, tothe reversal processing of photographic silver halide emulsions.

It is known that in the processing of photographic silver halideemulsions of color films, the exposed emulsions can be subjected to afirst(negative) developer which is a conventional black-and-whitedeveloper, followed by reversal reexposure and subsequent colordevelopment. Certain nucleating agents have been used in a solutionapplied following the first development step or in the second developersolution in place of the reversal reexposure step, but severaldisadvantages which limit their utility. For example, the mostsuccessful nucleating agents have been the boron compounds such asalkali metal borohydrides or borane, phosphine, arsine and stilbenecompounds described in U.S. Pat. Nos. 2,984,567 and 3,246,987. The amineboranes have been especially useful as nucleating agents. However, thesenucleating agents are not as stable as is desired. For example, theboranes tend to decompos'e when used in an acid stop solution fornucleation prior to the second development step. This requires theborohydrides and boranes to be packaged in alkaline solution such as adeveloper solution where they are still subject to decomposition byserial oxidation.

We have discovered that when stannous salt reducing agents for silverhalide are chelated and the resultant chelated stannous ions used asnucleating agents in the photographic reversal process, thedisadvantages of other nucleating agents are substantially avoided. Inparticular, when chelated stannous ion is used in the reversal colorprocess, unexpectedly significant improvement in structure of the colorimage is obtainable. More particularly, the chelated stannous salts havegood stability in both acid and alkaline solutions and, therefore, canbe packaged for use in acid or alkaline prebaths prior to the seconddevelopment step, or can be packaged in the second alkaline developercomposition.

The literature, such as British Pat. No. 500,796 and U.S. Pat. No.295,013, vaguely suggests, but does not clearly show, how stannoussalts, such as stannous chloride, can be successfully used in reversalprocesses for nucleation of the silver halide not developed in the firstdevelopment step. Our investigations show that an acid stannous chloridesolution, only at fairly high concentrations, will nucleate silverhalide and render it developable by a subsequent alkaline silver halidedeveloper solution. However, the stannous salt gradually undergoesaerial oxidation in the acid solution and the resulting stannic oxidedeposits on the emulsions as dirt which, particularly in colorprocesses, seriously reduces the quality of the color reproduction.Also, we have found that nonchelated stannous salt cannot beincorporated in alkaline developer solutions for nucleation anddevelopment of silver halide emulsion layers because an insolubleprecipitate at once forms and no nucleation occurs. On the other hand,when the chelated stannous salts are used as nucleating agents accordingto our invention, no insoluble product is formed in either acid oralkaline nucleating solutions and the dirt problem is avoided. lnaddition, a substantial improvement in photographicimage structure, suchas definition is obtainable.

In preparing the chelated stannous salt nucleating agents for use inphotographic reversal processes a polydentate ligand, such asNitrilo-N,N,N trimethylenephosphonic acid is dissolved in water andstannous salt, such as-stannous chloride, then added. At leaststoichiometric proportions, and preferably an excess of about percent ofthe ligand, are used to .prevent the formation of insoluble stanniccompounds in the solution through aerial oxidation or in the subsequentdevelopment solution where the chelated stannous ion is oxidized.Sufficient acid, preferably organic acid such as acetic acid, is addedto give a strongly acid solution of pH of about 2 to 7 and to providebuffering capacity. Useful buffering cnpuclty in obtained when thechelated stannous salt solution such contains about 0.1 to 5 molarconcentration of the acid. The resulting acid solution containingchelated stannous ion can then be employed as a stop bath following thenegative development step to nucleate the unexposed silver halide.Thereafter, treatment of the nucleated silver halide image with alkalinedeveloper solution produces the reversal positive image in black andwhite or color depending on the photographic system under consideration.

When the chelated stannous ion nucleating agents are employed in analkaline developer composition, a solution of stoichiometricproportions, preferably about l0 percent excess ligand, is prepared andthe stannous salt then added. This solution is then added to thedeveloper solution. Alternatively, these proportions of the ligand andstannous salt in solid form are dissolved in that order in the alkalinedeveloper solution. Otherwise, the formation of insoluble tin salt inthe solution can be expected.

Water-soluble stannous salts useful in preparing the chelated stannousion nucleating agents include, e.g. stannous halides such as stannouschloride, bromide and fluoride, and stannous acetate, stannous sulfate,stannous tartrate, etc.

A preferred class of heavy metal chelating agents useful for preparingthe chelated stannous ion nucleating agents includes organo phosphorouschelating agents. A useful class of chelating agents includes theaminopolymethylenephosphonic acid chelating agents and theirwatersoluble salts. These phosphonic acids have the general formulaRN(CH PO M,), wherein M represents a hydrogen atom or a cation whichimparts water solubility, such as alkali'metal atom (e.g. sodium,potassium, etc., ammonium, Pyridinium, triethanol'ammonium, triethylammonium, etc., and R represents an alkyl group, such as methyl, ethyl,propyl, isopropyl, butyl, etc. (e.g. an alkyl group containing from oneto four carbon atoms), an aryl group, such as phenyl, omand p-tolyl,oand p-carboxyl-phenyl (and water soluble salts thereof, such as sodium,potassium, etc.), an aralkyl group, such as benzyl-fi-phenethyl,o-acetamidobenzyl, etc. -(.e.;g. an aralkyl group containing from sevento nine carbon atoms), an alicyclic group,-such as cyclohexyl,cyclopentyl, etc. (e.g. an alicyclic group containing from five to sixcarbon atoms), .ora heterocyclic radical, such as a heterocyclylalkylgroup (e.g. pyrrolidylmethyl, pyrrolidylbutyl, benzothiazolymethyl,tetrahydroquinolylmethyl, etc.). The R group can be further substituted(especially where R represents an alkylgroup) with a radical, such ashydroxyl, --PO;M,, --CH,PO M,, or

N(CH,PO where M has the values given above,

chlorine, alkoxyl('e.g. methoxyl, ethoxyl, etc.), etc.

Representative useful compounds having this general formula are thefollowin g:

.Ethylenediamine-N,N,N',N-tetramethylenephosphonic acidNitrilo-N,N,N-trimethylenephosphonic acid l,2-cyclohexanediamine-N ,N,N,N -tetramethylenephosphonic acido-carboxyanilino-N,N-dimethylenephosphonic acidPropylamino-N,N-dimethylenephosphonic acidPropylamino-N,N-dimethylenephosphonic acid4-(N-pyrrolidino)butylamine-N,N- bis(methylenephosphonic acid)l,3-diaminopropanol-N,N,N' ,N tetramethylenephosphonic acidl,3-propanediam-ine-N,N,N',N'-tetramethylenephosphonic acid1,6-hexanediamine-N,N,N',N'-tetramethylenephosphonic acido-acetamidobenzylamino-N,N-dimethylenephosphonic acido-toluidine-'N,N-.dimethylenephosphonic acid2-pyridylamino-N',N'-dimethylenephosphonic acid A second class of organophosphorous chelating agents have the following general formulaRR,C(PO,M,), wherein R represents hydrogen, alkyl, aryl or aralkyl asdescribed above, or PO -,M,; R, represents hydrogen, hydroxyl, alkyl asabove or PO M and M represents the values given above.

Representative compounds having this formula are:

l-hydroxyethylidene-l l-diphosphonic acid ethylidene- 1 l l-triphosphonic acid l-hydroxypropylidene-l ,1 -diphosphonic acidl-hydroxy-2-phenylethylidenel l -diphosphonic acid It can be expectedthat the chelated stannous salts will differ in their ability tonucleate silver halide and, therefore, render it developable. lt isusually desirable to test each chelated stannous salt in thephotographic process under consideration to determine which give optimumresults.

In the reversal processing of multilayer, multicolor photo graphicelements, the first developer forms a negative blackand-white image.Photographic elements of the multilayer, multicolor type which do notcontain color-forming couplers in the silver halide emulsion layers thenare given a selective reversal reexposure of one silver halide emulsionlayer at a time followed by color development of the reversal exposedlayer with a color developer containing a color-forming coupler whichreacts with the oxidized p-phenylenediamine type developer to form theappropriate dye image corresponding to the positive silver image formed.After selective reversal reexposure and color development of one layer,a second layer is selectively reversal reexposed and color developed,then the third layer is selectively reversal reexposed and colordeveloped. The silver images and remaining silver halide are thenremoved by bleaching and fixing to leave the three dye images. Thechelated stannous ion nucleating agents of our invention are used toadvantage to eliminate the reversal reexposure required for the lastcolor developed layer. For this purpose, the nucleating agents areeither used in a nucleating bath with which the film is contacted afterthe second layer is color developed and before the third layer is colordeveloped, or alternatively, the nucleating agent is incorporated in thecolor developer used to develop the third layer.

Particularly useful color products for reversal processing according tothe method of our invention comprise a conventional support, such ascellulose esters, paper, glass, polyester film, polyvinyl acetal film,polycarbonate film, etc., having coated thereon at least two silverhalide layers which have been sensitized to particular regions of thespectrum. These emulsions have incorporated therein the color-formingcomponents or couplers, which combine with the oxidation products of thephotographic color developers, to produce the desired color images. Forexample, a typical color film, useful in practicing our inventioncomprises a support having coated thereon a red-sensitized photographicsilver halide emulsion having incorporated therein a coupler for thecyan image (e.g. a phenolic coupler), a green-sensitized photographicsilver halide emulsion having incorporated therein a coupler for themagenta image (e.g. pyrazolone coupler), and a blue-sensitizedphotographic silver halide emulsion containing a coupler for the yellowimage (e.g. a coupler containing an openchain ketomethylene group). Thephotographic element can also contain conventional interlayers andfilter layers, such as a yellow filter layer beneath the blue-sensitizedemulsion to prevent exposure by blue light to either the redorgreen-sensitized emulsion. Photographic color films of theabovedescribed type can be reversal processed by a technique requiringfewer steps than the selective reversal processing of the multilayercolor films mentioned above. According to our invention, for theprocessing of the emulsions having coupler compounds incorporatedtherein, it is only necessary to treat the exposed color film with theusual black-and-white developer for producing a negative silver image,followed by treatment with the aqueous chelated stannous ion nucleatingsolutions and followed by conventional color developer or,alternatively, followed by treatment with the color developer to whichhas been added one of the chelated stannous ion nucleating agents. Inthe practice of the present invention, any

of the conventional couplers as described in the prior art can be used.Couplers which are particularly useful in color developers for selectivereversal processes illustrated in example 4 below, include Couplers 1-64listed in columns 3-5of Spath U.S. Pat. No. 2,956,876, issued Oct. 18,l960. Couplers 65-77 described in the same patent in column 5 are usefulin the photographic silver halide emulsion layers of reversal processessuch as shown in example 2 below. Other couplers suitable for use in theemulsions include those described in Spence and Carroll U.S. Pat. No.2,640,776, issued June 2, 1953, Weissberger et al. U.S. Pat. No. 2,407,2l0, issued Sept. 3, 1946 and Weissberger et al. U.S. Pat. No. 2,474,294,issued June 28, 1949. Other couplers which can be used in the emulsionsinclude the acylamino-substituted couplers, as disclosed in Salminen andWeissberger U.S. Pat. No. 2,423,730, issued July 8, 1947.

The above organo phosphorous stannous ion chelates have unexpectedadvantages as compared with the aminopolycarboxylic acid stannous ionchelates, such as ethylenediamine tetraacetic acid stannous ion chelate.That is, the organo phosphorous chelates can be used over a wider rangeof concentrations. The significance of this range of concentrations isthat these chelates can be used at higher concentrations with the resultthat the nucleating solutions have considerably better stability underaerial oxidation because a larger excess can be tolerated withoutcausing undue development of silver halide. At these higherconcentrations the polyaminocarboxylic acid chelates tend to developsome of the silver halide rather than just nucleating it. Thus whilethese polyaminocarboxylic acid chelates can be used in the range ofconcentration of about 2 to 2,500 mgs. of stannous ion (calculated astin) per liter, the organo phosphonic acid nucleating agents can be usedin a range of about 2 to 7,000 mgs. per liter depending on thephotographic element in use. A further advantage resides in the factthat since larger amounts of the or gano phosphorous chelates can beused in making up the nucleating solutions more accurate solutions canbe prepared which results in more uniform processing of the photographicelements.

Example I -Black-and-White Reversal Process Using Chelated Stannous lonAn ordinary gelatin-silver bromoiodide emulsion layer is exposed to asubject and developed for 3 minutes in the following composition:

N-methyl-p-aminophenol sulfate 2.0 g. Sodium sulfite, anhydrous 90.0 g.Hydroquinone 8.0 g.

Sodium carbonate monohydrate 52.5 g. Potassium bromide 50 g. Water tomake I liter The developed film is then rinsed thoroughly with water andbleached for 2 minutes in a composition having the following formula:

Potassium bichrornate 9.4 g Sulfuric acid I20 cc Water to make I literThe bleached emulsion layer is then rinsed thoroughly with water andredeveloped for 3 minutes at 68 F. in the following solution:

N-methyl-p-aminophenolsulfate 0.6 Sodium sulfite, anhydrous 50.0 g.Hydroquinone 20.0 g Potassium bromide 8.0 g. Sodium thiocyunate 6.0 g.Sodium hydroxide 20.0 g.

Stannous chloride solution 20.0 cc. Water to make 1 liter *25 g. of(l-hydroxyethylidene-l.l-diphosphonic acid). 5.0 g. of SnCl=- 2H1O toone liter water.

The emulsion is then fixed out in the usual hypo fixing bath to obtain ahigh density black-and-white silver image in the emulsion layer.

The above process can also be carried out following the bleach step, bynucleating the unexposed silver halide with an acid solution of thechelated stannous salt such as the Nucleating Solution" shown in example2 below followed by development of the nucleated silver halide with theabove developer solution not containing the chelated stannous compound.

Example 2 -Reversal Color Process Using ChelatedStannous Ion Anincorporated coupler multilayer color film is provided comprising red,green and blue sensitive gelatin-silver halide emulsion layers on asupport, a yellow filter being coated between the blue and greensensitive emulsion layers. The emulsion layers contain reactivemethylene and phenolic coupler compounds reactive withp-phenylenediamine developing agents to form dyes of color complementaryto the sensitivity of the respective layers. The film in sheet or rollform is exposed to a colored subject and processed in a roller transportsystem such as shown in 11.8. Pat. No. 3,025,779 having staggered drivenrollers which advance the film through a series of tanks and a dryingchamber as follows:

Prehardener- 150 seconds, 95 F.

Dimcthoxytetrahydrofuran 4.3 g p-Toluenesulfinic acid, sodium salt 0.5 gSodium bisulfate 8.0 5 Potassium bromide 231 g Sodium acetate, anhydrous92.0 g Sodium sulfate, anhydrous 91.0 g Formalin, 37% 29.2 g. Water tomake 1 liter Sodium hydroxide or sulfuric as required to give pl'14-7.

Neutralizer-75 seconds, 97 F.

Sodium hydroxide 6.32 g. Acetic acid, glacial 10.5 g. Sodium bromide 2.0g. Hydroxylamine sulfate 18.0 g. Sodium sulfate, anhydrous 50.0 g. Boricanhydride 0.68 g. Water to make 1 liter First Developer- 150 seconds,100 F.

Quadrofos 2.00 g. Sodium sulfite, des. 47.00 g. Phenidone 0.35 g.Hydroquinone 5.50 g. Sodium carbonate, monohydrate 32.00 g. Sodiumbicarbonate 1.00 g. Boric anhydride 0.85 g. Sodium thiocyanate 1.38 g.Sodium bromide 1.30 g. Potassium iodide 0.013 g. Water to make 1 literFirst Stop75 seconds, 100 F.

Alternately, in preparing the formula above, instead of adding the above30 cc. solution of preformedchelated stannous ion, 15 gram ofl-hydroxyethylidene-l ,l-diphosphonic acid can be added followed by 3.0gram SnC1 21-1 0 and then add water to 1 liter.

Second Stop-75 seconds, 1 10 F.

Sodium bisulfate 10.0 g. Sodium acetate, anhydrous 13.0 g. Sodiumthiosulfate, anhydrous 31.86 g. Water to make 1 liter Wash-75 seconds,F.

Bleach-J5 seconds, 1 10 F.

Fix-75 seconds, 1 10 F.

Ammonium thiosulfate, 58% 163.0 cc. Sodium bisulfate, anhydrous l 1.0 g.Boric acid 8.0 g, Acetic acid, glacial 19.0 cc. Sodium hydroxide 8.0 g.Zirconium sulfate tetrahydrate 5.0 g. Water to make 1 liter Adjust to pH4.0

Wash-75 seconds, 90 F. Dry-150 seconds, F.

As a result of processing the color film in this manner, the chelatedstannous ion in the color developer nucleates the unexposed silverhalide in the emulsion layers and this silver halide is then developedby the color developing agent which then couples with the couplers inthe respective emulsion layers to form dye images at the sites ofdevelopment.

In the above process, the chelated stannous ion can be omitted from thecolor developer formula and the following solution used in place of theFirst Stop:"

Nucleatin Solution Sodium acetate, anhydrous 3.58 g. .Organo phosphorouschelating agent 1.5 g.

Acetic acid, glacial 28.85 g.

Water to make 1 liter Same chelating agent as the color developer aboveor Nitrilo-N,N N- trimethylenephosphonic acid.

The unexposed silver halide is thus nucleated and is developed by thesubsequent color developer.

An advantageous and unexpected result of using the chelated stannous ionin the above color processes is noted as additional quantities of filmare processed through the solutions. That is, according to the mechanismof the process mentioned above, during the color development reactionthe chelated stannous ion present in the color developer solution, orany which is introduced by the acid prebath before color development, isoxidized to chelated stannic ion which does not precipitate from thedeveloper solution. Stannous salt (nonchelated) cannot be used in thecolor developer solution instead of chelated stannous ion because thesolution immediately becomes dirty and useless and the dirt is notremovable from the emulsion surface. Similarly, if nonchelated stannoussalt is used in the acid prebath instead of chelated stannous ion, dirtgradually builds up in the prebath and deposits on the emulsion surfacefrom which it is not removable. Also, any nonchelated tin salt carriedover from the prebath by the emulsion layers is immediately precipitatedas dirt in the subsequent alkaline developer solution.

Example 3-Comparison of Reversal Processes Using Chelated Stannous Saltand Borane Nucleating Agents The process of example 2 is carried outexcept replacing the chelated stannous salt in the color developer by.073 g. of tert. butylamineborane. A useful subtractively coloredpositive reproduction of the subject is obtained. However, when theimage structure is compared with that obtained in example 2 using thechelated stannous ion for nucleation, it is found that the example 2process using chelated stannous ion produces dye images wherein the redcolors contain less cyan contamination, i.e. the red colors are muchbrighter. Also, the example 2 process yields blue colors having lessyellow contamination, i.e. the blue colors are brighter. In addition,the cyan colors are more saturated and there is a significantimprovement in definition in images obtained in the example 2 process.

Example 4 -Selective Reversal Color Process Using Chelated Stannous IonA conventional multilayer color film is provided having superimposed ona transparent support in order red, green and blue light-sensitivegelatin-silver halide emulsion layers free of color-forming couplers. Ayellow filter layer is positioned between the blue and green sensitiveemulsion layers. After exposure to a colored subject, the film isdeveloped in the usual MQ black-and-white developer solution, washed,reexposed through the base to red light and developed with aconventional color developer solution containing a phenolic cou pler forthe cyan dye image. After washing, the film is reexposed to blue lightfrom the emulsion side and developed as usual in a color developercontaining a reactive methylene type coupler which forms the yellow dyeimage. After washing, the film is treated at 83 F. for one minute and 13seconds in the following magenta reversal bath:

Water 700.0 cc. Quadrofos 4.0 g. Sodium hydroxide 3.0 g. Stannouschloride solution 60.0 cc. Water to make 1 liter *25 gramsNitrilo-N,N,N-trimethylenephosphofic acid and 5.0 grams SnClz Hz to 1liter of water,

This results in nucleation of the unexposed silver halide in the WaterSulfuric acid, (cone.)

2.l ml.

Trisodium phosphatelZl-Ifl 40.0 g. Sodium sulfite (desiccated) 5.0 g.Sodium thiocyanate 1.0 g. Z-Amino-S-diethylaminotoluene 2.60 g.hydrochloride Citrazinic acid 0.70 g. Ethylenediamine 3.0 g.Polyethylene glycol 0.25 g. Sodium sulfate (anhydrous) 50.0 g. Sodiumhydroxide 0.32 g. 2,4,6-(trichlorophcnyl)-3-p- 1.60 g.nitroanilino-2-pyrazoline-5-one Hexylene glycol 5.0 ml. Sodium bromide0.5 g. Potassium iodide (0.1%) 7.5 ml. Water to make I liter The film isthen washed, bleached with ferricyanide solution for rehalogenating thesilver as usual followed by washing and fixing with hypo solution. Thedye images obtained in the film have a good density and contrast. Thereis no evidence of dirt in the solutions or on the film even after aconsiderable amount of film has passed through the solutions.

If desired, the above process can be carried out in the manner ofexample 2 by omitting the above magenta reversal bath and incorporatingthe following solution into the above magenta color developercomposition: 20 cc. of a solution containing 25 grams of Nitrilo-N,N,N-

.trimethylenephosphonic acid and 5.0 grams SnCl '2H 0 made to 1 literwith water. Thus, the undeveloped silver in the green sensitive layer isboth nucleated and color developed by the developer solution.

In general, the amount of chelated stannous ion nucleating agent used inthe color reversal process as illustrated in the above examples is suchthat the undeveloped silver halide is nucleated fully or to the requiredextent under the processing conditions of time and temperature. Theamount of silver halide initially present in the emulsion layer orlayers will, to some extent, determine the solution concentration ofstannous ion; but generally the amount of silver halide left after thefirst development step of the reversal process determines the stannousion concentration under the conditions of operation, and is that amountof stannous ion sufficient to nucleate the available silver halide.Thus, if too much nucleating agent is used, some silver halide isreduced leaving an insufficient amount of nucleated silver halide foruse in the subsequent color development step. In a black-and-whitereversal process coneentration of the nucleating agent is not ascritical. Accordingly, when the nucleating agents are used in an acidprebath before color development at about -l25 F. for about 30-90seconds as shown in example 2, for average emulsion layers about 2 to7,000 mgs. per liter of stannous ion, calculated as tin, is useful, e.g.about 3.8 mg. to 13.3 g. SnCl '2BY20 is useful in making a liter of thechelated stannous ion solution. Thus, at the higher concentrations,nucleation of silver halide takes place but some silver halide in anouter emulsion layer may be reduced with concomitant loss in dye densityin that layer.

When chelated stannous ion is used in a color developer in processessuch as shown in examples 2 and 4 with average emulsion layers, about2to 7,000 mgs. per liter as tin is also useful at about 80 F.- F. whenprocessing for the time necessary to complete development. Inblack-and-white processes illustrated in example 1, also about 2 to7,000 mgs. stannous ion as tin per liter of the developer solution isuseful and about 2 to 7,000 mgs. stannous ion as tin per liter when thechelate is employed in an acid prebath before the blackand-whitedevelopment step. Accordingly, it will be understood that the optimumconcentrations of the chelated stannous ion in the solutions is bestdetermined by experiment with the particular single or multilayerphotographic elements in use under the conditions of operation. Asdiscussed above, an excess of the ligand component of the chelate shouldbe present, e.g., about 10 percent excess.

The chelated stannous ion nucleating agents in accordance with theformula given above are used as nucleating agents as disclosed inexamples 1 and 2 especially either in an acid prebath or color developerfor development of incorporated coupler color products, or in an acidprebath or color developer solution in selective reversal colorprocesses such as described in example 4.

Color development, as described in the above examples, can be carriedout using any of the well-known color-forming developing agents whichare capable of coupling with the color-forming components or couplers.Particularly useful color-forming developing agents are thep-phenylenediamines and substituted derivatives thereof. Typical of suchcolorforming developing agents are the sulfonamide-substitutedpphenylenediamines disclosed in Weissberger US. Pat. No. 2,548,574,issued Apr. 10, 1951, the substituted p-phen ylenediamines disclosed inWeissberger et a1. U.S. Pat. Nos. 2,552,240; 2,552,241 and 2,552,242,issued May 8, 1951, and the substituted p-phenylenediamines disclosed inWeissberger et al. US. Pat. No. 2,566,271, issued Aug. 28, 1951. Otherphenylenediamine color-forming developing agents can be employed to likeadvantage in the process of our invention.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

We claim:

1. In a photographic reversal process wherein a silver halide emulsionlayer is exposed to an image, the emulsion layer is developed in theregions of exposure with a first silver halide developing solution, areversal positive image is obtained by nucleating the unexposed silverhalide of the emulsion layer by contacting the layer with a chemicalnucleating agent to render it developable with a second silver halidedeveloping solution and developing the resulting nucleated silverhalide, the improvement for obtaining better photographic reproductionand definition comprising nucleating the unexposed silver halide bycontacting it with an aqueous solution of organo phosphorous chelatedstannous ion silver halide nucleating agent.

2. In a photographic reversal color process wherein a photographicelement containing at least two silver halide emulsion layersdifferentially sensitized to different spectral regions is exposed to acolored image, images are developed in the emulsion layers in theregions of exposure using a first silver halide developing solution, andreversal positive colored images are obtained by nucleating theunexposed silver halide of the emulsion layers by contacting the layerswith a chemical nucleating agent to render at least one of themdevelopable with a second silver halide color developing solution, anddeveloping the resulting nucleated silver halide to form the positivecolored images, the improvement for obtaining better color reproductionand definition comprising nucleating the unexposed silver halide bycontacting it with an aqueous solution of organo phosphorous chelatedstannous ion silver halide nucleating agent.

3. In a photographic reversal color process wherein a photographicelement containing at least two silver halide emulsion layersdifferentially sensitized to different spectral regions and colorforming coupler compounds is exposed to a colored image, images aredeveloped in the emulsion layers in the regions of exposure using afirst silver halide developing solution, and reversal positive coloredimages are obtained by nucleating the unexposed silver halide of theemulsion layers by contacting the layers with a chemical nucleatingagent to render them developable with a second silver halide colordevelopin solution, and developing the resulting nucleated silver hall eto form the positive colored images, t e Improvement for obtainingbetter color reproduction and definition comprising nucleating theunexposed silver halide by contacting it with an aqueous solution oforgano phosphorous chelated stannous ion silver halide nucleating agent.

4. The process of claim 3 wherein the unexposed silver halide isnucleated by treatment with an acid solution of the chelated stannousion prior to treatment of the emulsion layers with the color developingsolution.

5. The process of claim 3 wherein chelated stannous ion is present in adeveloping solution containing color developing agent to nucleate theunexposed silver halide and render it developable by the colordeveloping agent.

6. In a photographic reversal color process wherein a photographicelement containing at least two silver halide emulsion layersdifferentially sensitized to different spectral regions and free ofcolor-forming coupler compounds is exposed to a colored image, silverimages are developed in the emulsion layers in the regions of exposureusing a first silver halide developing solution, reversal positivecolored images are obtained by consecutive reversal reexposure of theemulsion layers except for the last one and developing the reexposedlayers separately with color developing solutions containingcolor-forming coupler compounds, and the unexposed silver halide of saidone emulsion layer is then nucleated by contacting it with a chemicalnucleating agent followed by developing the resultant nucleated silverhalide with a color developing solution containing a color-formingcoupler compound, the improvement for obtaining better colorreproduction and definition comprising using organo phosphorous chelatedstannous ion as the chemical nucleating agent.

7. The process of claim 6 wherein the chelated stannous ion is presentin the color developing solution used for development of the nucleatedsilver halide.

8. The process of claim 3 wherein the photographic element containsthree superimposed silver halide emulsion layers sensitive respectivelyto the red, green and blue regions of the spectrum and each emulsionlayer contains a coupler compound for formation of a dye image in thelayer of a color complementary to the sensitivity of emulsion layer, andthe nucleation of the silver halide is effected by the use of an organophosphorous stannous ion silver halide nucleating agent present in thecolor developing solution.

9. An aqueous solution for the nucleating of photographic silver halideemulsion layers containing organo phosphorous chelated stannous ionsilver halide nucleating agent and sufficient organic acid to give a pHof about 2 to 7 and provide buffering capacity.

10. A solution for nucleating and developing photographic silver halideemulsion layers comprising alkali, a silver halide developing agent andorgano phosphorous chelated stannous ion silver halide nucleating agent.

11. The developing solution of claim 10 wherein the developing agent isa primary aromatic amino silver halide developing agent.

12. The developing solution of claim 11 further containing a couplercompound reactive with the oxidation product of the developing agent toform a dye.

2. In a photographic reversal color process wherein a photographicelement containing at least two silver halide emulsion layersdifferentially sensitized to different spectral regions is exposed to acolored image, images are developed in the emulsion layers in theregions of exposure using a first silver halide developing solution, andreversal positive colored images are obtained by nucleating theunexposed silver halide of the emulsion layers by contacting the layerswith a chemical nucleating agent to render at least one of themdevelopable with a second silver halide color developing solution, anddeveloping the resulting nucleated silver halide to form the positivecolored images, the improvement for obtaining better color reproductionand definition comprising nucleating the unexposed silver halide bycontacting it with an aqueous solution of organo phosphorous chelatedstannous ion silver halide nucleating agent.
 3. In a photographicreversal color process wherein a photographic element containing atleast two silver halide emulsion layers differentially sensiTized todifferent spectral regions and color forming coupler compounds isexposed to a colored image, images are developed in the emulsion layersin the regions of exposure using a first silver halide developingsolution, and reversal positive colored images are obtained bynucleating the unexposed silver halide of the emulsion layers bycontacting the layers with a chemical nucleating agent to render themdevelopable with a second silver halide color developing solution, anddeveloping the resulting nucleated silver halide to form the positivecolored images, the improvement for obtaining better color reproductionand definition comprising nucleating the unexposed silver halide bycontacting it with an aqueous solution of organo phosphorous chelatedstannous ion silver halide nucleating agent.
 4. The process of claim 3wherein the unexposed silver halide is nucleated by treatment with anacid solution of the chelated stannous ion prior to treatment of theemulsion layers with the color developing solution.
 5. The process ofclaim 3 wherein chelated stannous ion is present in a developingsolution containing color developing agent to nucleate the unexposedsilver halide and render it developable by the color developing agent.6. In a photographic reversal color process wherein a photographicelement containing at least two silver halide emulsion layersdifferentially sensitized to different spectral regions and free ofcolor-forming coupler compounds is exposed to a colored image, silverimages are developed in the emulsion layers in the regions of exposureusing a first silver halide developing solution, reversal positivecolored images are obtained by consecutive reversal reexposure of theemulsion layers except for the last one and developing the reexposedlayers separately with color developing solutions containingcolor-forming coupler compounds, and the unexposed silver halide of saidone emulsion layer is then nucleated by contacting it with a chemicalnucleating agent followed by developing the resultant nucleated silverhalide with a color developing solution containing a color-formingcoupler compound, the improvement for obtaining better colorreproduction and definition comprising using organo phosphorous chelatedstannous ion as the chemical nucleating agent.
 7. The process of claim 6wherein the chelated stannous ion is present in the color developingsolution used for development of the nucleated silver halide.
 8. Theprocess of claim 3 wherein the photographic element contains threesuperimposed silver halide emulsion layers sensitive respectively to thered, green and blue regions of the spectrum and each emulsion layercontains a coupler compound for formation of a dye image in the layer ofa color complementary to the sensitivity of emulsion layer, and thenucleation of the silver halide is effected by the use of an organophosphorous stannous ion silver halide nucleating agent present in thecolor developing solution.
 9. An aqueous solution for the nucleating ofphotographic silver halide emulsion layers containing organo phosphorouschelated stannous ion silver halide nucleating agent and sufficientorganic acid to give a pH of about 2 to 7 and provide bufferingcapacity.
 10. A solution for nucleating and developing photographicsilver halide emulsion layers comprising alkali, a silver halidedeveloping agent and organo phosphorous chelated stannous ion silverhalide nucleating agent.
 11. The developing solution of claim 10 whereinthe developing agent is a primary aromatic amino silver halidedeveloping agent.
 12. The developing solution of claim 11 furthercontaining a coupler compound reactive with the oxidation product of thedeveloping agent to form a dye.